Utility vehicles, such as tractors, include a main hydraulic oil reservoir and at least one auxiliary reservoir. On current production tractors, the auxiliary reservoirs have air vent lines that communicate back to the upper end of the main reservoir. With such an arrangement, when a towed implement, such as a wagon with a dump cylinder is coupled to the tractor hydraulic system, oil will be drawn out of the main reservoir. In such situations, the main reservoir oil level will always be below the auxiliary reservoir oil level, and the main reservoir can be emptied while unused oil remains in the auxiliary reservoir. If the main reservoir oil level gets too low, no more oil can be supplied to the dump cylinder, and extra, unused oil will remain in the auxiliary reservoir.
Previously, EH valves and extra pumps have been used to insure the maximum amount of oil is used from the auxiliary reservoir. However, such components are costly and require control software and wiring harness integration and place an extra hydraulic load on the tractor.